1. Field of the Invention
The present invention relates generally to video tape reproducing systems, and more particularly to a high speed tape reproduction system which simultaneously reads different portions of audio and video signals stored on a master by means of a multi-head optical master system, then processes and applies the detected signals to a multi-head rotary head drum recording system which reassembles and records the audio and video signals on a video tape, in their original order, in a fraction of the time normally required for reproduction.
This application is related to copending application Ser. No. 07/095,491 filed Sept. 11, 1987 entitled "Multiple Slave Video Tape Reproduction System", assigned to the assignee of the present invention.
2. Brief Description of the Prior Art
Prior art video reproduction systems are typically comprised of a master, such as a high quality video tape recorder (player), connected to a multiple number of slave recorders, such as off the shelf consumer VHS or BETA video tape recorders. As the master reads the audio and video signals, comprising the recorded program, at the standard playback speed, one or a number of slaves record the perform onto blank video tape at the same recording speed. To increase reproduction productivity, as many as 100 slave recorders will be connected to each master. Naturally, the greater the number of slaves combined with each master, the greater the number of tapes produced during each production period.
Combining a large number of slave recorder to each master system can be rather expensive. Apart from the costs associated with purchasing and maintaining as many as 100 slave recorders, the quantity of recorders alone require that adequately sized facilities be available to house the recorders, as well as air conditioning to keep the recorders operable. In addition, each new recording requires the previously recorded tape to be removed and the next blank tape to be installed in each slave recorder. Thus, unless a large number of operators or automated loaders are available, unloading and loading as many as 100 recorders can add a significant amount of time to the overall recording period. In addition, when a large number of operators are utilized, many will have nothing to do while the recording is being made, further adding to the cost of each recording unnecessarily. Thus, prior art recording systems may only be able to record as few as 300 two-hour programs in an eight hour production cycle.
The audio recording industry has long recognized that recording at any rate faster than the standard playback rate will enhance productivity and lower production costs. However, while audio duplicating systems are known to record as fast as 64 times the playback speed, it is much more complicated to increase the speed of video recording. In audio recording, a stationary head records the information onto the tape as the tape is pulled across the surface of the head, at a speed proportional to the signal input rate to the head. If the tape passes across the surface of the head at five times normal speed, the frequency of the input signal must by five times the normal signal frequency. Higher recording signal frequencies are generally achieved by passing the tape across the master playback head at five times normal speed.
In video tape recording, much more is required to increase the recording speed than raising the output signal frequency and proportionally increasing the speed at which the tape passes the head. VHS and BETA tape recorders typically utilize two recording heads mounted 180 degrees out of phase to each other on the circumference of a rotary head drum. The magnetic recording tape is wrapped around a portion of the drum and kept in contact with the circular surface of the drum. When recording, the drum rotates in one direction with respect to the tape so that the two heads move in a wave like motion and produce a series of helical scan recordings on the tape. To increase the recording speed of a prior art recorder, both the longitudinal speed of the tape and rotational speed of the head drum must be increased accordingly.
At 1800 revolutions per minute (RPM), the rotational and horizontal movement of the head drum is controllable, however, at double the recording speed, where the head drum rotates at 3600 RPM, and at quadruple the recording speed, where the head drum rotates at 7200 RPM, the rotational movement of the head drum becomes unstable. For each increase in recording speed, there is a square or cube multiplication of technical problems associated with the speed increase. Likewise, for each increase in the rotational speed of the drum, there must be a proportional increase in the video signal frequency. If the playback signal frequency is at 5 MHz, the recording signal frequency of a recording made at four times (4X) speed must be 20 MHz.
Electronics circuits capable of handling high frequency signals are both difficult and expensive to design and build. Where a standard playback speed recording system can be purchased for as little as $500.00, a two times (2X) speed recording system, in order to be cost effective, can cost no more than $1000.00, and a 4X speed recording system can cost no more than $2000.00. In general, due to the high costs associated with producing high speed recording systems with previously available recording equipment, the cost of prior art high speed recording systems have far exceeded competitive and cost justifiable levels.
The use of as many as four heads in the head drum of recorders is well known in the prior art, at least with regard to applications in which the recording speed is the same as the playback speed. Tsuruta, U.S. Pat. No. 4,014,985, issued Sept. 30, 1986, discloses a signal switching system for selectively supplying each of the four recording heads of the head drum with appropriate video signals. Although Tsuruta discloses that a four-head rotary head drum can be used in place of a two-head drum, Tsuruta also discloses that a number of mechanical and electrical conditions must be met for the four-head drum to record a video signal compatible with standard two-head drum recorders. One condition is that the tape must be wrapped around the peripheral surface of the head drum at an angular range of approximately 270 degrees. A second condition is that the tape speed must be selected so that the tape travels by one track pitch during one field period in which one rotary video head rotates by 270 degrees.
In order to meet the above conditions, Tsuruta disclosed that the diameter of the head drum must be reduced to 2/3 the diameter of a standard two-head drum and that an elaborate head signal switching system must be employed, rather than the standard practice of applying continuous recording current to the two recording heads. Thus, recording current is supplied to one head as it makes a 270 degree rotational pass, while the two immediately following heads are supplied no recording current, then recording current is supplied to the third immediately following head, etc. A signal switching system that provides accurate phase control synchronization for a reduced diameter four-head drum similar to that disclosed in Tsuruta is disclosed in Yoshino et al U.S. Pat. No. 4,609,952, issued Sept. 2, 1986.
Other increased speed recording systems, utilizing a variety of recording techniques, have been developed over the years to overcome the problems associated with increasing tape and head drum speeds. One such system is disclosed by Cooley et al U.S. Pat. No. 4,320,486, issued Mar. 16, 1982, in which an optical storage medium is used as an intermediate transfer medium from which recorded information signals may be reproduced at speeds of 2 to 200 times normal playback speed. However, as with all such systems before, such high speed recording systems have greater application to audio recording, where the heads are stationary, then to video recording, where heads must be rotated faster to accommodate the increased signal frequency supplied to the slave recorder.